Gas sensor control apparatus

Abstract

An O 2 sensor has a sensor element, which includes a solid electrolyte layer and a pair of electrodes. The solid electrolyte layer is held between the electrodes, which includes an atmosphere side electrode and an exhaust side electrode. A constant current circuit is installed in an electric path, which connects between the atmosphere side electrode and a ground, to induce a flow of a predetermined constant electric current between the electrodes through the solid electrolyte layer. When the sensor element generates an electromotive force, the constant current circuit conducts an electric current, which is generated while using the electromotive force of the sensor element as an electric power source, to induce the flow of the predetermined constant electric current between the electrodes in an electromotive force range, which is equal to or larger than an electromotive force of the sensor element generated at a stoichiometric air-to-fuel ratio.

What is claimed is: 
     
       1. A gas sensor control apparatus for a gas sensor, the gas sensor outputting an electromotive force signal corresponding to an air-to-fuel ratio of an exhaust gas of an internal combustion engine and including an electromotive force cell, the electromotive force cell having a solid electrolyte body and a pair of electrodes, wherein the solid electrolyte body is held between the pair of electrodes, the pair of electrodes including a reference side electrode and an exhaust side electrode, the reference side electrode becoming a positive side at a time of outputting an electromotive force from the electromotive force cell, and the exhaust side electrode becoming a negative side at the time of outputting the electromotive force from the electromotive force cell, the gas sensor control apparatus comprising:
 a current conduction regulating device that is installed in an electric path that is connected to the electromotive force cell to induce a flow of a predetermined constant electric current between the exhaust side electrode and the reference side electrode through the solid electrolyte body in the electromotive force cell, wherein: 
 the current conduction regulating device conducts the predetermined constant electric current that is generated while using the electromotive force of the electromotive force cell as an electric power source to induce the flow of the predetermined constant electric current between the exhaust side electrode and the reference side electrode when the electromotive force of the electromotive force cell is in a corresponding electromotive force range which that is equal to or larger than a predetermined electromotive force of the electromotive force cell that is generated at a theoretical air-to-fuel ratio of the exhaust gas; 
 the current conduction regulating device includes:
 a resistor that is installed in the electric path that is connected to the electromotive force cell; and 
 an operating device that is operable to hold a voltage of one end portion of the resistor at a predetermined reference voltage, wherein the one end portion of the resistor is a side of the resistor closest to the reference side electrode of the electromotive force cell; and 
 
 a voltage value of the predetermined reference voltage is smaller than a voltage value of the electromotive force of the electromotive force cell generated at the theoretical air-to-fuel ratio. 
 
     
     
       2. The gas sensor control apparatus according to  claim 1 , wherein
 a resistance value of the resistor is in a range of 50Ω to 500 Ω. 
 
     
     
       3. The gas sensor control apparatus according to  claim 1  further comprising
 a voltage changing device that changes the predetermined reference voltage. 
 
     
     
       4. A gas sensor control apparatus for a gas sensor, the gas sensor outputting an electromotive force signal corresponding to an air-to-fuel ratio of an exhaust gas of an internal combustion engine and including an electromotive force cell, the electromotive force cell having a solid electrolyte body and a pair of electrodes, wherein the solid electrolyte body is held between the pair of electrodes, the pair of electrodes including a reference side electrode and an exhaust side electrode, the reference side electrode becoming a positive side at a time of outputting an electromotive force from the electromotive force cell, and the exhaust side electrode becoming a negative side at the time of outputting the electromotive force from the electromotive force cell, the gas sensor control apparatus comprising:
 a current conduction regulating device that is installed in an electric path that is connected to the electromotive force cell to induce a flow of a predetermined constant electric current between the exhaust side electrode and the reference side electrode through the solid electrolyte body in the electromotive force cell; and 
 a control device programmed to control the current conduction regulating device, wherein: 
 the current conduction regulating device conducts the predetermined constant electric current that is generated while using the electromotive force of the electromotive force cell as an electric power source to induce the flow of the predetermined constant electric current between the exhaust side electrode and the reference side electrode when the electromotive force of the electromotive force cell is in a corresponding electromotive force range that is equal to or larger than a predetermined electromotive force of the electromotive force cell that is generated at a theoretical air-to-fuel ratio of the exhaust gas; 
 the gas sensor control apparatus is applied to an exhaust gas purifying device of the internal combustion engine; 
 the exhaust gas purifying device is installed in an exhaust device of the internal combustion engine and includes a catalyst that purifies NOx, which is a lean component of the exhaust gas, and a rich component of the exhaust gas; 
 the gas sensor is installed in the exhaust device at a location which is in an intermediate portion of the catalyst or on a downstream side of the catalyst, to sense the air-to-fuel ratio of the exhaust gas after purification of the exhaust gas with the catalyst; 
 the catalyst has a conversion characteristic, which indicates a relationship between the air-to-fuel ratio and a catalytic conversion efficiency of the catalyst; 
 the conversion characteristic of the catalyst includes a second air-to-fuel ratio point, which is a point of starting an outflow of the NOx from the catalyst and is located on a rich side of a first air-to-fuel ratio point that forms an equilibrium point for the rich component and oxygen; and 
 the control device controls the current conduction regulating device such that the current conduction regulating device induces the flow of the predetermined constant electric current having a current value, which corresponds to a difference between the first air-to-fuel ratio point and the second air-to-fuel ratio point of the catalyst. 
 
     
     
       5. The gas sensor control apparatus according to  claim 4 , wherein
 the current conduction regulating device induces the flow of the predetermined constant electric current having the current value, which is required to shift an equilibrium point of a gas reaction around the exhaust side electrode of the electromotive force cell to the second air-to-fuel ratio point or an adjacent point that is adjacent to the second air-to-fuel ratio point. 
 
     
     
       6. The gas sensor control apparatus according to  claim 5 , wherein
 the current conduction regulating device induces the flow of the predetermined constant electric current having the current value, which is required to shift the equilibrium point of the gas reaction around the exhaust side electrode of the electromotive force cell to a rich side of the second air-to-fuel ratio point. 
 
     
     
       7. The gas sensor control apparatus according to  claim 1 , further comprising:
 a current sensing arrangement that senses a current value of an actual electric current that flows in the electromotive force cell; 
 an abnormality determining section that determines whether an abnormality is present in the current conduction regulating device based on the current value of the actual electric current, which is sensed with the current sensing arrangement, when the flow of the predetermined constant electric current is induced by the current conduction regulating device; 
 an electromotive force determining section that determines whether a voltage value of the electromotive force of the electromotive force cell is smaller than a predetermined voltage value; and 
 a nullifying section that nullifies abnormality determination of the abnormality determining section when the electromotive force determining section determines that the voltage value of the electromotive force of the electromotive force cell is smaller than the predetermined voltage value. 
 
     
     
       8. The gas sensor control apparatus according to  claim 7 , wherein
 the predetermined voltage value is set at the electromotive force determining section based on a temperature of the electromotive force cell. 
 
     
     
       9. The gas sensor control apparatus according to  claim 1 , wherein
 the current conduction regulating device does not conduct an electric current when the electromotive force of the electromotive force cell is less than the predetermined electromotive force of the electromotive force cell that is generated at the theoretical air-to-fuel ratio of the exhaust gas.